Method of erecting a tower on the sea-bed, in deep water

ABSTRACT

This invention relates to a method of erecting a tower on the sea-bed in deep water where said tower is formed by a submerged pontoon resting on the bed and by an upper platform between which is arranged a bracing pylon secured to said pontoon and wherein the platform rests on a plurality of piles driven through the pylon. According to the invention, a floating pontoon is built which is equipped with a platform having apparatus for lifting it with respect to said pontoon and this pontoon is brought to a sheltered area where the water is shallow and is anchored afloat in that position. The pylon is then constructed on said pontoon after having brought auxiliary columns to rest on the bed through the pontoon these columns then forming guide and support members for auto-lifting apparatus for said platform, and the platform is raised on these columns as the construction of the pylon progresses. The piles may be driven through inclined tubular pillars associated with the pylon.

States Patent [191 Loire [75] inventor: Rene Loire, Paris, France [73] Assignee: Compagnie (lenerale DEquipement Maritime Prllersent, Paris, France [22] Filed: Apr. 30, 1973 [2]] Appl. No.: 355,483

{30] Foreign Application Priority Data May 8, 1972 France 16378 [52] U.S. Cl. 61/465 [51] int. Cl lEtlZd 21/00, E02b 17/00 [58] Field of Search 61/465, 50,46; 114/.5

[56] References Cited UNITED STATES PATENTS 2,621,485 12/1952 Ross 61/465 2,771,747 11/1956 Rechtin 61/465 Get. 8, 11974 [57] ABSTRACT This invention relates to a method of erecting a tower on the seabed in deep water where said tower is formed by a submerged pontoon resting on the bed and by an upper platform between which is arranged a bracing pylon secured to said pontoon and wherein the platform rests on a pluraiity of piles driven through the pylon. According to the invention, a floating pontoon is built which is equipped with a platform having apparatus for lifting it with respect to said pontoon and this pontoon is brought to a sheltered area where the water is shallow and is anchored afloat in that position. The pylon is then constructed on said pontoon after having brought auxiliary columns to rest on the bed through the pontoon these columns then forming guide and support members for auto-lifting apparatus for said platform, and the platform is raised on these columns as the construction of the pylon progresses. The piles may be driven through inclined tubular pillars associated with the pylon.

'7 Claims, 12 Drawing Figures METHOD OF ERECTING A TOWER ON THE SEA-BED, llN DEEP WATER The present invention relates to a method of erecting a tower on the seabed, in deep water, which is intended to support apparatus for drilling for, and exploiting, oil fields.

Platforms intended for the exploitation of oilfields and set up in the open sea are known. Generally speaking, they are manufactured in parts in dry dock, the

parts being fitted together on the drilling site itself. This assembly requires a great deal of handling equipment which cannot be other than floating and is thus subject to the sea conditions encountered locally. Furthermore, the production and drilling equipment can only be installed on such platforms after they have finally been placed in position, using handling apparatus which is, once again, subject to the swell and to sea conditions.

It is a primary object of the invention to enable these drawbacks to be alleviated as a result of a simplification in the procedure of placing a platform in position on the open sea.

To this end, the invention consists in a method of erecting a tower on the seabed, in deep water, which is intended to support apparatus for drilling for, and exploiting, oil fields, where said tower being formed by a submerged pontoon resting on the bed and by an upper platform between which is arranged a bracing pylon secured to said pontoon, said platform resting on a plurality of piles driven through said pylon, in particular through sloping tubular pillars therein. According to the invention, a floating pontoon is built which is equipped with a platform having means for raising itself in relation to the pontoon and then, after having first brought the pontoon to a sheltered area where the bed is shallow and anchored it there afloat, the pylon is constructed on the pontoon after auxiliary columns have been placed against the bed through the pontoon, said auxiliary columns then forming members for guiding and supporting the auto-lifting means for the platform, which is then raised on the said columns as the construction of the pylon progresses.

After having provided supporting means for certain columns under the lower face of the pontoon, all the columns are then raised (thus allowing the pontoon to float) so that the said support means make contact with the lower face of the pontoon, and the platform is locked on the columns by its lifting means. 7

After the tower so constructed has been brought, while floating, to the chosen site, and after it has been provisionally moored using a plurality of anchor points, the columns which do not have support means are released from the restraint placed on them by their associated lifting means, and the columns then drop onto the seabed and bury themselves therein by their own weight under the guidance of the tower. The pontoon is then filled with ballast so that it slowly submerges, along with the pylon, its descent being guided by the columns embedded in the sea-bed and governed, in the initial stage, by the lifting means associated with these columns, until the platform is floating at sea level.

In a second stage, submersion is controlled by the auto-lifting means associated with the columns which are equipped with support means in contact with the lower face of the pontoon and supporting it, the columns which first dropped to the sea-bed being at the same time raised and disengaged from the sea-bed until the pontoon touches the undersea floor.

Next, after the platform has been raised on the columns to the desired height and after guide members have been arranged on at least some of the columns intended to serve as guides in setting up the inclined piles and the drilling means, piles are driven from the platform into the undersea floor. in particular through sloping tubular pillars in the pylon, the vertical piles being formed by the auxiliary columns provided with the support means and the said piles are permanently secured to the platform and the pylon.

Advantageously, the sloping piles are formed by the columns which are not equipped with supporting means. these being extracted in sections from the group of auxiliary columns.

Finally, the section of each of the piles located between the platform and the pylon is reinforced with a tube of the same length as the said section which is inserted into the pile and secured to the latter after it has been drained.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate the various phases of one specific method by way of example, and also depicting a finished tower and in which:

FIG. I shows a first phase of the method according to the invention,

FIG. 2 is a view alongfin FIG. ll,

FIG. 3 shows a second phase of the method,

FIG. 4 shows a third phase of the method,

FIG. 5 shows a fourth phase of the method.

FIG. 6 shows an enlarged view of area A of FIG. 5,

FIG. FIG. FIG. FIG.

7 shows a fifth phase of the method, 8 shows a sixth phase of the method, 9 shows a seventh phase of the method, lll) shows an eighth phase of a method,

FIG. 11 shows a ninth phase of the method, and

FIG. 12 shows a view of a tower erected in accordance with the method.

Referring now to the drawings, and firstly to FIG. ll, there areseen, arranged in a sheltered area, a floating pontoon I supportinga platform 2 through both of which pass a certain number of columns 3 which can be locked in position at the platform 2 by auto-lifting means 5 for lifting the platform, these meansalso making possible relative movement between the platform 2 and the columns 3 in the vertical direction.

FIG. 2 brings out two groups within the columns 3, which are marked 3a and 3b, these being for example four columns 3a in the centre and eight columns 312 on the outside, and two groups of auto-lifting means 5a and 5b associated with the two groups of columns 3a and 312 respectively.

In FIG. 3, the platform 2 is shown in a position to which it has been raised by its auto-lifting means 5 on the columns 3, which rest on the sea-bed, while a pylon 4i is shown in the course of being constructed on the pontoon l, the handling means required for this construction being shown diagramatically by cranes marked 10, 10a and 10!). In particular, pylon 4 is shown here in a frusto-conical shape with an octagonal base, each angle of which is formed by a sloping tubular pillar marked 4a.

FIG. 4 is aschematic view of the tower which has been built up in a sheltered area being towed to the site selected for its installation. It will be noted that the crane 10 has remained in position on the platform 2.

FIG. 5 illustrates a phase of the method in which the tower is provisionally moored by anchor points 6, while the eight columns 3b have been embedded under their own weight in the under-sea floor. The four columns 3a are held in the raised position by the auto-lifting means associated with them and these columns have support means, marked 11 in FIG. 6 which, with the columns 3a in this position, are held in contact with the lower face of the pontoon 1.

FIG. 7 shows a first phase in the submergence of tower under the guidance of columns 3b, and FIG. 8 shows the end of the submergence, with the platform 2 afloat and the columns 3b no longer in contact with the sea-bed.

FIG. 9 shows the platform 2 in the process of lifting itself up the columns 3, the pontoon l resting on the sea-bed.

In FIG. 10 is shown a guide-member 7 which is attached to the columns 3a between the pylon 4 and the platform 2 and which serves as a guide for positioning piles 8 in the sloping tubular pillars 4a of the pylon 4, which piles are driven into the bed.

FIG. 11 shows one of the piles 8 reinforced by a tube 9 inserted in the pile 8 and secured to the latter at the platform 2 and at a sloping tubular pillar 4a belonging to the pylon 4.

FIG. 12 shows the tower set up in position, with the piles 8 secured to the pylon 4 and the platform 2, while the columns 3a are driven into the tinder-sea floor and permanently attached to the platform 2.

The way in which the various phases of the method link up, which is explained below, will assist in comprehending the invention while bringing out its advantages.

After the pontoon and the platform 2 have been built in the work-shops, e.g., of a dock yard, they are fitted with columns 3 and auto-lifting means 5 as shown in FIG. 1, and are towed, one on top of the other, to a sheltered area where the water is shallow.

The pylon 4 is then constructed, as shown in FIG. 3, after the columns 3, which then serve as support and guide members for the auto-lifting means for the platform 2, have beenbrought to rest on the bed, the platform being raised as the construction of the pylon 4 progresses. The construction is carried on using floating handling machinery 110a and 10b and the crane 10 which is permanently installed on the platform.

Once this phase is completed, the columns 3 are raised using the means 5, and the platform 2 rests on the pylon 4 so that the tower so produced may be towed to the point at which it is to be installed.

In FIG. 4, which shows the towing, the vertical position of the tower may be noted, which is of advantage for its final installation since it eliminates any handling operations on the open sea prior to placing it in position.

The next phase ofthe method consists firstly in mooring the tower provisionally at the spot at which it is to be installed by anchor points 6 shown in FIG. 5. The columns 312 are then released by freeing them of the restraint of the auto-lifting means 512 seen in FIG. 2. These columns drop to the sea-bed and embed themselves in it under their own weight. Care is taken at this time to have the columns 3a in a position such that the support means 11 shown in FIG. 6 are kept in contact with the lower face of the pontoon l. The platform 2 is thus held securely to the pylon 4.

The pontoon l is then filled with ballast to submerge it, as shown in FIG. 7. It descends under the guidance of columns 3b and is governed by the auto-lifting means 5b associated with these columns. When the platform 2 is afloat, the descent of the pontoon l continues under the guidance of columns 31; and is then governed by auto-lifting means 50 which support the pontoon 1 via columns 3a and support means II. At a certain depth, the columns 3b are raised to prevent the swell thrusting against the pylon 4 and the pontoon 1 from exerting excessively large bending stresses on the columns 3b. The lowering process is then continued along the lines shown in FIG. 8 until the pontoon l is touching the under-sea floor.

FIG. 9 shows how the platform 2 then lifts itself up all the columns 3 using all the auto-lifting means 5, which become available once the pontoon 1 has been lowered. This raising has the ancillary effect of embedding all the columns 3 in the under-sea floor and of stabilising the tower.

When the platform 2 is at the desired height, at least 1 guide member marked 7 in FIG. 10 is fixed to the columns 3a between the platform and the pylon 4, its purpose being, on the one hand, to serve as a guide for setting up the sloping piles 8 in the tubular pillars 4a and, on the other hand, to form a bracing member for the drilling tubes which will be set up subsequent to the final installation of the tower.

The columns 3b are then withdrawn in sections using the crane 10. These columns 312 then form the piles 8 which are driven into the floor through the pillars 4a of the pylon 4.

After each pile 8 has been reinforced by means of a tube 9 arranged inside the pile 8 between the platform 2 and the pillar 4a, as shown in FIG. 11, all the piles 8 are secured to the pillar 4a and the platform 2, while the columns 30 are also driven into the floor and permanently connected to the platform 2. FIG. 12 is a schematic view of the tower thus installed.

Such a method enables the platform 2 to be held constantly in a horizontal position, which is advantageous for the progress of the assembly operations. In effect, handling means may thus be permanently installed on this platform, in particular one or more cranes which may become service cranes for drilling and exploitation. These handling means do away with the use of floating cranes which, being subject to sea conditions, are of limited use. Using this method, assembly work may thus go on under practically any prevailing conditions.

Furthermore, part of the drilling equipment may advantageously be installed on the platform before it is even launched. 7

Finally, the method described above is extremely useful for setting up towers of large size. To give a specific idea of what is concerned, in a trial being carried out, the pylon 4 rises to 84 m above the pontoon l, which forms a base 85m square, the platform 2 being situated 30m above the sea at a site where the depth is from to m.

I claim:

1. The method of erecting a tower on a sea-bed, in deep water, wherein the completed tower consists of a submerged pontoon resting on the seabed, an upper platform, and a bracing pylon secured to the pontoon and located below said upper platform, said platform being supported on a plurality of piles driven through the pylon; said method comprising the steps of forming a floating pontoon and a platform associated therewith in superimposed relation; providing said pontoon and platform with at least two sets of columns extending therebetween in sliding relation to the pontoon and platform; and providing said platform with auto-lifting apparatus associated with each of said columns; transporting said pontoon and superimposed platform over water to a sheltered area where the water is shallow; anchoring said pontoon afloat in that position on the water; and thereafter constructing the pylon on said pontoon below said platform by first dropping one of said sets of columns through said pontoon until they come to rest on the sea-bed through the pontoon, said one set of columns then forming guide and support members for said auto-lifting apparatus for said platform, and then raising said platform on said one set of columns as the construction of the pylon progresses; providing support means on the other of said two sets of columns at predetermined positions to engage the lower face of said pontoon; raising all of said columns with said autolifting apparatus after said pylon is constructed to positions out of contact with the sea-bed to allow said pontoon to float and until said support means come into contact with the lower surface of said pontoon; and locking said platform on said columns by operating said auto-lifting apparatus to engage the platform with the upper end of the pylon.

2. The method according to claim 1, including the step of driving said piles through inclined tubular pillars in said pylon.

3. The method of erecting a tower on the sea-bed in deep water, wherein the completed tower consists of a submerged pontoon resting on a seabed, an upper platform, and a bracing pylon secured to said pontoon and located below said upper platform, said platform being supported on a plurality of piles driven through inclined tubular pillars in said pylon, and said platform being equipped with auto-lifting means and at least two sets of auxiliary columns arranged vertically through the platform, the pylon, and the pontoon, and locked on said pontoon by auto-lifting means, with one of said sets of auxiliary columns being provided with support means located below the lower face of said pontoon and adapted to be placed in contact with the said face during the erection of said tower; said method comprising the steps of, transportion the tower assembly, consisting of the pontoon, platform and pylon therebetween to the selected site while afloat on the pontoon, provisionally mooring the platform in the sea by means of a plurality of anchor points, freeing the columns in the set of said columns which are not provided with said support means from the restraint of said autolifting means thereby dropping those columns to the seabed and causing them to embed themselves in the sea-bed under their own weight, said columns being guided during this dropping step in a vertical direction by said pontoon and platform, thereafter filling said pontoon with ballast to slowly submerge the pontoon and said pylon, while guiding the descent of the pontoon and the pylon with said columns embedded in the seabed and controlling the descent, in an initial stage, by the operation of the auto-lifting means associated with the columns embedded in the sea-bed until the platform is at sea-level, and, in a second stage by operation of the auto-lifting means associated with the set of columns equipped with the support means, said support means being in contact with the lower face of said pontoon to support the pontoon on the set of columnsequipped with the support means; the columns which initially dropped in to the seabed being simultaneously raised and disengaged from the sea-bed until said pontoon touches the under-sea floor.

4. The method according to claim 3 including the steps of raising said platform on said columns to a desired height, after said pontoon is submerged to the seabed, arranging guide members on at least some of said columns for serving as guides for setting in piles and for drilling means; thereafter driving inclined piles into the under-sea floor from said platform, through inclined tubular pillars in said pylon, and driving said set of columns provided with the support means into the undersea floor to form vertical piles, and permanently securing all of said piles to said platform and said pylon.

5. The method according to claim 4, wherein said step of driving said inclined piles includes the step of forming the piles from the columns from the set of columns not equipped with support means, after extracting that set of columns in sections from the pontoon and platform.

6. The method according to ciaim 4, including the step of reinforcing the section of each of said piles situated between said platform and said pylon with a tube of the same length as said section, by placing the tube into the interior of said pile and securing the tube to the pile.

7. The method according to claim 5, including the step of reinforcing the section of each of said piles situated between said platform and said pylon with a tube of the same length as said section, by placing the tube into the interior of said pile and securing the tube to the pile. 

1. The method of erecting a tower on a sea-bed, in deep water, wherein the completed tower consists of a submerged pontoon resting on the sea- bed, an upper platform, and a bracing pylon secured to the pontoon and located below said upper platform, said platform being supported on a plurality of piles driven through the pylon; said method comprising the steps of forming a floating pontoon and a platform associated therewith in superimposed relation; providing said pontoon and platform with at least two sets of columns extending therebetween in sliding relation to the pontoon and platform; and providing said platform with auto-lifting apparatus associated with each of said columns; transporting said pontoon and superimposed platform over water to a sheltered area where the water is shallow; anchoring said pontoon afloat in that position on the water; and thereafter constructing the pylon on said pontoon below said platform by first dropping one of said sets of columns through said pontoon until they come to rest on the sea-bed through the pontoon, said one set of columns then forming guide and support members for said auto-lifting apparatus for said platform, and then raising said platform on saId one set of columns as the construction of the pylon progresses; providing support means on the other of said two sets of columns at predetermined positions to engage the lower face of said pontoon; raising all of said columns with said auto-lifting apparatus after said pylon is constructed to positions out of contact with the sea-bed to allow said pontoon to float and until said support means come into contact with the lower surface of said pontoon; and locking said platform on said columns by operating said auto-lifting apparatus to engage the platform with the upper end of the pylon.
 2. The method according to claim 1, including the step of driving said piles through inclined tubular pillars in said pylon.
 3. The method of erecting a tower on the sea-bed in deep water, wherein the completed tower consists of a submerged pontoon resting on a sea- bed, an upper platform, and a bracing pylon secured to said pontoon and located below said upper platform, said platform being supported on a plurality of piles driven through inclined tubular pillars in said pylon, and said platform being equipped with auto-lifting means and at least two sets of auxiliary columns arranged vertically through the platform, the pylon, and the pontoon, and locked on said pontoon by auto-lifting means, with one of said sets of auxiliary columns being provided with support means located below the lower face of said pontoon and adapted to be placed in contact with the said face during the erection of said tower; said method comprising the steps of, transportion the tower assembly, consisting of the pontoon, platform and pylon therebetween to the selected site while afloat on the pontoon, provisionally mooring the platform in the sea by means of a plurality of anchor points, freeing the columns in the set of said columns which are not provided with said support means from the restraint of said auto-lifting means thereby dropping those columns to the sea-bed and causing them to embed themselves in the sea-bed under their own weight, said columns being guided during this dropping step in a vertical direction by said pontoon and platform, thereafter filling said pontoon with ballast to slowly submerge the pontoon and said pylon, while guiding the descent of the pontoon and the pylon with said columns embedded in the sea- bed and controlling the descent, in an initial stage, by the operation of the auto-lifting means associated with the columns embedded in the sea-bed until the platform is at sea-level, and, in a second stage by operation of the auto-lifting means associated with the set of columns equipped with the support means, said support means being in contact with the lower face of said pontoon to support the pontoon on the set of columns equipped with the support means; the columns which initially dropped in to the sea- bed being simultaneously raised and disengaged from the sea-bed until said pontoon touches the under-sea floor.
 4. The method according to claim 3 including the steps of raising said platform on said columns to a desired height, after said pontoon is submerged to the sea-bed, arranging guide members on at least some of said columns for serving as guides for setting in piles and for drilling means; thereafter driving inclined piles into the under-sea floor from said platform, through inclined tubular pillars in said pylon, and driving said set of columns provided with the support means into the undersea floor to form vertical piles, and permanently securing all of said piles to said platform and said pylon.
 5. The method according to claim 4, wherein said step of driving said inclined piles includes the step of forming the piles from the columns from the set of columns not equipped with support means, after extracting that set of columns in sections from the pontoon and platform.
 6. The method according to claim 4, including the step of reinforcing the section of each of said piles situated between said platform and said pylon with a tube of the same length as said secTion, by placing the tube into the interior of said pile and securing the tube to the pile.
 7. The method according to claim 5, including the step of reinforcing the section of each of said piles situated between said platform and said pylon with a tube of the same length as said section, by placing the tube into the interior of said pile and securing the tube to the pile. 